Expose geojson PROPERTIES to whereeval

This commit adds a new Lua variable named PROPERTIES that provides
the GeoJSON 'properties' member as a decoded Lua table.

For example, take this geojson object.

{
  "type": "Feature",
  "geometry": { "type": Point, "coordinates": [ -112, 33 ] },
  "properties": { "speed": 85 }
}

Now the Tile38 command can be used to filter on object

SCAN fleet WHEREEVAL 'return PROPERTIES.speed > 75'

Author: tidwall

internal/server/scanner.go

@@ -271,16 +271,18 @@ func (sw *scanWriter) fieldMatch(o *object.Object) (bool, error) {
 	}
 	if len(sw.whereevals) > 0 {
 		fieldNames := make(map[string]field.Value)
+		var props string
 		if objIsSpatial(o.Geo()) {
 			z := extractZCoordinate(o.Geo())
 			fieldNames["z"] = field.ValueOf(strconv.FormatFloat(z, 'f', -1, 64))
+			props = gjson.Get(o.Geo().Members(), "properties").Raw
 		}
 		o.Fields().Scan(func(f field.Field) bool {
 			fieldNames[f.Name()] = f.Value()
 			return true
 		})
 		for _, whereval := range sw.whereevals {
-			match, err := whereval.match(fieldNames)
+			match, err := whereval.match(fieldNames, o.ID(), props)
 			if err != nil {
 				return false, err
 			}

internal/server/token.go

@@ -9,6 +9,7 @@ import (
 
 	"github.com/tidwall/tile38/internal/field"
 	lua "github.com/yuin/gopher-lua"
+	luajson "layeh.com/gopher-json"
 )
 
 const defaultSearchOutput = outputObjects
@@ -158,18 +159,33 @@ func luaSetField(tbl *lua.LTable, name string, val field.Value) {
 	tbl.RawSetString(name, lval)
 }
 
-func (whereeval whereevalT) match(fieldsWithNames map[string]field.Value) (bool, error) {
+func (whereeval whereevalT) match(fieldsWithNames map[string]field.Value,
+	id string, props string) (bool, error,
+) {
 	fieldsTbl := whereeval.luaState.CreateTable(0, len(fieldsWithNames))
 	for name, val := range fieldsWithNames {
 		luaSetField(fieldsTbl, name, val)
 	}
+	var lprops lua.LValue
+	if props != "" {
+		var err error
+		lprops, err = luajson.Decode(whereeval.luaState, []byte(props))
+		if err != nil {
+			lprops = lua.LNil
+		}
+	}
+	// lua.LTString
 	luaSetRawGlobals(
 		whereeval.luaState, map[string]lua.LValue{
-			"FIELDS": fieldsTbl,
+			"ID":         lua.LString(id),
+			"FIELDS":     fieldsTbl,
+			"PROPERTIES": lprops,
 		})
 	defer luaSetRawGlobals(
 		whereeval.luaState, map[string]lua.LValue{
-			"FIELDS": lua.LNil,
+			"ID":         lua.LNil,
+			"FIELDS":     lua.LNil,
+			"PROPERTIES": lua.LNil,
 		})
 
 	whereeval.luaState.Push(whereeval.fn)